The present invention relates generally to diagnostic imaging systems using computed tomography and, more particularly, to an x-ray generator and slip ring for a CT system such that a stationary inverter supplies power to the slip ring for transference to a rotating high voltage tank for creating a voltage potential across a rotating x-ray tube.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
The x-ray generator of a CT system is located within the gantry and, as such, rotates around an imaging bore during data acquisition. The x-ray generation generally includes an x-ray tube, data acquisition system, and arcuate shaped detector arrays. This well-known configuration is shown in FIG. 1. As illustrated, the x-ray generator and slip ring configuration 2 includes an x-ray tube 3, a high voltage (HV) tank 4, and inverter 5 operationally connected to a slip ring 6. Tube 3, HV tank 4, and inverter are each connected and secured to a rotating base 7 that supports each during rotation of the gantry. External to the rotating base 7 and electrically connected to slip ring 6 is a power distribution unit (PDU) 8 that is stationary and therefore does not rotate with tube 3, tank 4, and inverter 5. Inverter 5 is typically fed with a DC voltage, for example, 650 VDC, and generates an AC voltage waveform, for example, approximately 300 VAC, at a specified frequency, e.g. 20 k–50 kHz. The AC voltage is then fed to the HV tank 4 which has a transformer and rectifiers (not shown) that develop a DC HV potential. The HV potential is then applied to the x-ray tube 3. Since the HV tank and inverter are positioned on the rotating base, the power to the inverter is easily transferred to the rotating side across relatively low voltage (˜650 VDC) slip ring 6. Rotating base 7 is also designed with one or more auxiliary devices that may include auxiliary power devices, generally referenced 4a. 
With this configuration, the inverter 5 is positioned on the rotating base 7 and therefore rotates during data acquisition. A circuit schematic of the inverter is shown in FIG. 2. The inverter 5 includes a number of power switches 9 (e.g. IGBTs) arranged in an H-configuration. Connected to one output of the H-configuration is an LC circuit forming a resonant circuit 10. The output of the resonant circuit 10 and the other output of H-configuration 9 is fed to HV tank 4. The HV tank includes a transformer 11 connected to a rectifier and filter circuit 12 to create a voltage potential across monopolar x-ray tube 3. Inverter 5, HV tank 4, and tube 3 are positioned on the rotating side of slip ring 6. As such, with this known configuration, a relatively low DC voltage is supplied to the slip ring 6 which is then transferred to inverter 5 for conditioning.
This placement of the inverter on the rotating side of the slip ring has a number of drawbacks. For example, rotating at higher gantry speeds is problematic because the mass of the components on the rotating side as well as their associated rotational forces limit gantry speed. Additionally, if gantry speed is increased, the power requirements of the x-ray generator also increase so as to maintain a constant SNR. As such, the size and mass of the x-ray generator components must also be increased to provide the required power. Further, the size of the x-ray generator components in current CT systems have resulted in a cantilevered configuration out from the rotating base. This cantilevered configuration adds a torque on mounting brackets used to secure the components as well as increases the forces placed on the retaining brackets. All of which limit gantry rotational speed.
Therefore, it would be desirable to design an x-ray generator architecture that reduces the size and weight constraints on the rotating base of a CT system thereby allowing for an increase in gantry rotation speed without a deprivation in power delivery to the x-ray tube.